In the field of exterior and interior illumination of motor vehicles, light-emitting diodes (LEDs) are being increasingly used instead of conventional incandescent bulbs, particularly for tail lights and brake lights, since LEDs have a longer service life, better efficiency in converting electrical energy into radiation energy in the visible spectral range, lower thermal emission characteristics, and reduced space requirements.
The practical advantages of utilizing LED lamps instead of incandescent bulbs are many. The operational lifetime (in this case, defined as continuous illumination service) of a LED is on the order of ten years or over 50,000 hours, whereas incandescent bulbs often burn out after about 2,000 hours of service. Additionally, LED lamps are considerably more robust. When exposed to mechanical shocks or stresses, chemical stresses (e.g., such as may be caused by cleaning chemicals or road salt), or the presence of or temperature variations often encountered in an outdoor environment, LEDs are less likely to fail than incandescent lamps. This attribute is especially important when the lamp is utilized in motor vehicles wherein perishable filaments of incandescent lamps frequently break due to constant vibrational motion. Further, incandescent and fluorescent lamps are constructed with fragile glass exterior casings whose breakage compromises the operational utility of the lamp. In contrast, the solid state LED lamp has no filaments to break and is usually housed within a durable plastic casing, thereby exhibiting a high level of imperviousness to extreme outdoor environmental stresses. A further advantage of LEDs is that they have a more rapid turn-on time and generate less heat per lumen of light relative to conventional lighting products. The compact size and flexibility of form of LEDs offer still further advantages in relaxing space constraints and providing freedom to the designer to adopt new styling configurations, such as may be useful to create brand recognition.
A LED is a solid-state device having a PN junction semiconductor diode that emits light when a current is applied. LEDs operate at relatively low current and voltage and emit substantially less heat per lumen than standard halogen or high intensity discharge (HID) lamps. The LED can be easily encapsulated in a resin material to protect the device and thus make it durable and long lasting. The use of semiconductor LEDs solves many problems associated with incandescent bulbs including, but not limited to, high entrapped heat, limited lamp longevity, frequent lamp replacement and higher current operation.
Recently, higher brightness white light LED lamps have become increasingly affordable to manufacture and now present attractive substitutes for incandescent, halogen, and high intensity discharge (xenon discharge lamp) (HID) vehicle lamp sources. There are currently three methods for producing LEDs that emit white light. The first and second methods use a single blue, violet or UV LED die that emits a single wavelength of radiation, either with a phosphoric coating thereon or a phosphoric layer between the encapsulant and the lens, with the phosphor converting portions of the light into longer wavelengths that lead to the perception of white light. The third method uses independent red, blue, and green dies in the same package. When all three are powered, white light is perceived.
Although more attractive as the illuminating source for the reasons enumerated above, LEDs have not become the favored light source for headlights and other lighting sources. For example, light distribution characteristics (particularly for low beam headlamps) of vehicle headlamps have been standardized, requiring a horizontal line that reduces glare on oncoming vehicles. Additionally, a minimum center luminous intensity of 8000 cd or more in the front view facilitates a driver's far distance visibility. These requirements are not readily satisfied using the single element reflector cup package known in the art.
Headlamps including multiple LED packages have been proposed to achieve desired levels of total brightness and/or directionality. Each LED package includes a LED die plus a dedicated lead frame, reflector cup, encapsulant, and lens. The presence of multiple packages, particularly those redundant packages required to switch directionality, substantially increases the cost of the overall headlamp assembly and consumes significant volume, thus reducing packaging efficiency and reducing design options.
Accordingly, there is a continuing need in the art for improved multi-LED light source assemblies that minimize lamp package quantities and footprint while enabling directional switching for vehicular and/or other lighting applications.